Industrial effluent disposal at a glance

What is industrial effluent?

Industrial effluent is any wastewater generated by an industrial
activity. An industrial activity is any process that involves the
creation of any object or service for profit – from the garage that
services your car to the café where you buy your lunch.

All industry,
no matter how big or small, produces dirty water that must be cleaned:
industrial effluent.

Using a combination of mechanical and biological means, BIO-SYSTEMS
can assist with the improvement of most industrial effluent discharge
quality by reducing and degrading (and in some cases removing) organic
waste present in the effluent before it leaves the premises and is
released to a municipal treatment plant or to the environment.

Managing industrial effluent

The aim is to get the effluent as close to DWAF Standard discharge
quality (or that stipulated by your local authority) as quickly and as
economically as possible.

Most effluent streams should be subjected to the following list of treatment activities, typically in the sequence shown below:

1. Solids removal

Interceptors, grease/fat traps and screens are used to remove solids such as grit, pips, skins, curds and twigs.

2. pH (acidity/alkalinity) is adjusted

Inorganic chemicals (acids and alkalis) are often used in food processing. The pH of the effluent to be treated must be adjusted to within a range in which the microbes are comfortable to operate, promoting the breakdown of complex organic wastes.

This controls corrosion (from harsh chemical residues), which has very expensive consequences.

3.
Primary settlement

Where the effluent is ‘stilled’ in a large, deep tank to allow any remaining heavy solids to drop to the floor to form a sludge that can be withdrawn periodically via scouring valves. Fats and oils, which have a low specific gravity (i.e. lighter than water) float to form a scum that is easily removed by a sweep arm.

4. Replacing ‘good’ bacteria

Depleted/destroyed by organic inhibitors such as heat and chemicals (for example, acids and caustic soda). The bacteria restore the biological balance and help accelerate the degrading process. BIO-SYSTEMS has identified and isolated various strains of bacteria that work optimally in specific effluent streams under certain conditions.

As a result, our biological products are targeted to break down specific pollutants. For example, BIO-SYSTEMS B220R, degrades fats, oils and greases (FOG) in the food industry. The inoculated bacteria will also help to metabolize excess Nitrate (N) and Phosphate (P) present in the effluent, which are often residues of processing chemicals, washing powders and household detergents.

5. Anaerobic digestors

These are closed chambers, often bee-hive shaped or multi chambered (septic tanks) where soft COD (organic waste) is degraded without the influence of oxygen. They help remove soft (readily degradable) COD from the wastewater. There is no need for energy input (electricity), but this is a slow process by simple bacteria.

6. Aerobic-activated sludge reactors/basins

Are equipped with energy-consuming aerators to entrain atmospheric oxygen into the effluent under treatment. Aeration is key to the whole clean-up process. Oxygen catalyses bacteria to degrade hard and soft organic wastes.

By replacing oxygen driven out by heat during the manufacturing process, conditions for a viable biomass population are promoted.

Aerobic activity is quicker than anaerobic. However, there is a downside: the cost of ‘input’ electrical energy and the maintenance cost – both of time and money – of moving parts.

7. Secondary settlement happens in a clarifyer

Following the activated sludge reactor/aeration basin, it is customary for the treated effluent to be allowed to settle in a clarifier.

This is a deep (about four metres), circular tank with an inverted conical bottom where any remaining organic wastes - free floating or emulsified - rise to the surface and are skimmed off by a slowly-rotating, centre-pivoted bridge arm and returned to the reactor for further processing.

Many clarifiers also have a slow moving scraper to dislodge pollutants that may have settled on the submerged internal circular wall. The inverted conical bottom facilitates the gravitational fall of solids to the central scouring valve at the lowest point.

8. The maturation river

This is a rectangular, shallow pond through which the effluent is snaked along narrow channels and where the final degradation of remaining COD, or ‘polishing’ takes place under atmospheric influences.

9. On to the oxidation ponds

A three (or sometimes more) lagoon system enables progressive maturation or oxidation of the effluent. Here it is ‘polished’ by ultraviolet radiation from the sun. Design depths are 1.2-1.5 meters to permit UV penetration.

10. Finally, chlorine contact

This happens before discharge to the environment, which could be a natural watercourse or an irrigation storage reservoir (large factories may use their treated wastewater to irrigate a golf course or public planting). Gaseous chlorine is ‘contacted’ to the treated effluent as it leaves the works to kill off any pathogens before discharge. The efficacy of the gas is temporary. It kills microbes on contact, but rapidly degrades and will not affect the quality of the water course into which it is discharged (chlorine breaks down very quickly under sunlight, which is why it is sold in supermarkets in opaque bottles).

11. Membrane Technology (MBR)

Some effluent plants use MBR, which employs a large expanse of micro filters (usually made from a special textile) mounted in replaceable pockets. These take the place of the clarifiers, maturation rivers and settlement lagoons. MBR is especially relevant where space is at a premium (built-up areas with high land value). MBR units are becoming a popular option as they are highly efficient and can consistently produce effluent to a high standard (potable if need be). The initial high civils cost must be weighed against low maintenance and footprint considerations. MBR units are particularly suited to manufacturing and processing plants in urban areas.